Note 5 - Derivative and Other Hedging Instruments (Details Textual) - Short [Member] $ in Millions	Dec. 31, 2024 USD ($) $ / item	Dec. 31, 2023 USD ($) $ / item
Five Year Treasury Note Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	106.3	108.77
Derivative, Fair Value, Net | $	$ 332.2	$ 458.5
Ten Year T-Note Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	108.75
Derivative, Fair Value, Net | $	$ 101.7
Ten Year Ultra Futures [Member]
Derivative, Forward Price (in USD per Per Share) | $ / item	111.31	112.89
Derivative, Fair Value, Net | $	$ 36.2	$ 361.3